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Just

A library of zero-dependency npm modules that do just one thing. A guilt-free alternative to those bulkier utility libraries. Ideal for PWA development or whenever bytes are precious.

Build status

Jump To API

We welcome contributions. Please follow our contribution guidelines.

Try 🍦

A REPL for every utility (powered by RunKit)

Read 📚

ES and CJS modules available for every utility

All packages support ES module or Common JS syntax without requiring transpilation

// esm (node / bundler)
import clone from 'just-clone'; 

// esm (native browser code)
import clone from './node_modules/just-clone/index.mjs'; 

// cjs
const clone = require('just-clone'); 

TypeScript

We're in the process of adding TypeScript definitions and tests to every Just utility. You're welcome to help us get there! Here's an example PR.

You can verify new TypeScript definitions by running yarn test-types (This also gets run as part of the yarn test script)

Browser Support 💻

Data based on available saucelabs test browsers. It's likely Just is also fully supported by some older versions not verifiable via saucelabs.

Chrome Safari Firefox Edge Node Mobile Safari Android
yes yes yes 12 6+ iOS 8+ Android OS 5+

The Modules 📦

Collections

just-diff

source

🍦 Try it

npm install just-diff
yarn add just-diff

Return an object representing the difference between two other objects Pass converter to format as http://jsonpatch.com

import {diff} from 'just-diff';

const obj1 = {a: 4, b: 5};
const obj2 = {a: 3, b: 5};
const obj3 = {a: 4, c: 5};

diff(obj1, obj2);
[
  { "op": "replace", "path": ['a'], "value": 3 }
]

diff(obj2, obj3);
[
  { "op": "remove", "path": ['b'] },
  { "op": "replace", "path": ['a'], "value": 4 }
  { "op": "add", "path": ['c'], "value": 5 }
]

// using converter to generate jsPatch standard paths
import {diff, jsonPatchPathConverter} from 'just-diff'
diff(obj1, obj2, jsonPatchPathConverter);
[
  { "op": "replace", "path": '/a', "value": 3 }
]

diff(obj2, obj3, jsonPatchPathConverter);
[
  { "op": "remove", "path": '/b' },
  { "op": "replace", "path": '/a', "value": 4 }
  { "op": "add", "path": '/c', "value": 5 }
]

// arrays
const obj4 = {a: 4, b: [1, 2, 3]};
const obj5 = {a: 3, b: [1, 2, 4]};
const obj6 = {a: 3, b: [1, 2, 4, 5]};

diff(obj4, obj5);
[
  { "op": "replace", "path": ['a'], "value": 3 }
  { "op": "replace", "path": ['b', 2], "value": 4 }
]

diff(obj5, obj6);
[
  { "op": "add", "path": ['b', 3], "value": 5 }
]

// nested paths
const obj7 = {a: 4, b: {c: 3}};
const obj8 = {a: 4, b: {c: 4}};
const obj9 = {a: 5, b: {d: 4}};

diff(obj7, obj8);
[
  { "op": "replace", "path": ['b', 'c'], "value": 4 }
]

diff(obj8, obj9);
[
  { "op": "replace", "path": ['a'], "value": 5 }
  { "op": "remove", "path": ['b', 'c']}
  { "op": "add", "path": ['b', 'd'], "value": 4 }
]

just-diff-apply

source

🍦 Try it

npm install just-diff-apply
yarn add just-diff-apply

Apply a diff object to an object. Pass converter to apply a http://jsonpatch.com standard patch

  import diffApply from 'just-diff-apply';

  const obj1 = {a: 3, b: 5};
  diffApply(obj1,
    [
      { "op": "remove", "path": ['b'] },
      { "op": "replace", "path": ['a'], "value": 4 },
      { "op": "add", "path": ['c'], "value": 5 }
    ]
  );
  obj1; // {a: 4, c: 5}

  const obj2 = {a: 3, b: 5};
  diffApply(obj2,
    [
      { "op": "move", "from": ['a'], "path": ['c']},
    ]
  );
  obj2; // {b: 5, c: 3}

  // using converter to apply jsPatch standard paths
  // see http://jsonpatch.com
  import {diffApply, jsonPatchPathConverter} from 'just-diff-apply'
  const obj3 = {a: 3, b: 5};
  diffApply(obj3, [
    { "op": "remove", "path": '/b' },
    { "op": "replace", "path": '/a', "value": 4 }
    { "op": "add", "path": '/c', "value": 5 }
  ], jsonPatchPathConverter);
  obj3; // {a: 4, c: 5}

  // arrays (array key can be string or numeric)
  const obj4 = {a: 4, b: [1, 2, 3]};
  diffApply(obj4, [
    { "op": "replace", "path": ['a'], "value": 3 }
    { "op": "replace", "path": ['b', 2], "value": 4 }
    { "op": "add", "path": ['b', 3], "value": 9 }
  ]);
  obj4; // {a: 3, b: [1, 2, 4, 9]}

  // nested paths
  const obj5 = {a: 4, b: {c: 3}};
  diffApply(obj5, [
    { "op": "replace", "path": ['a'], "value": 5 }
    { "op": "remove", "path": ['b', 'c']}
    { "op": "add", "path": ['b', 'd'], "value": 4 }
  ]);
  obj5; // {a: 5, b: {d: 4}}

just-compare

source

🍦 Try it

npm install just-compare
yarn add just-compare

Compare two collections

import compare from 'just-compare';

// primitives: value1 === value2
// functions: value1.toString == value2.toString
// arrays: if length, sequence and values of properties are identical
// objects: if length, names and values of properties are identical
compare([1, [2, 3]], [1, [2, 3]]); // true
compare([1, [2, 3], 4], [1, [2, 3]]); // false
compare({a: 2, b: 3}, {a: 2, b: 3}); // true
compare({a: 2, b: 3}, {b: 3, a: 2}); // true
compare({a: 2, b: 3, c: 4}, {a: 2, b: 3}); // false
compare({a: 2, b: 3}, {a: 2, b: 3, c: 4}); // false
compare([1, [2, {a: 4}], 4], [1, [2, {a: 4}]]); // false
compare([1, [2, {a: 4}], 4], [1, [2, {a: 4}], 4]); // true
compare(NaN, NaN); // true

just-clone

source

🍦 Try it

npm install just-clone
yarn add just-clone

Deep copies objects and arrays

// Deep copies objects and arrays, doesn't clone functions

import clone from 'just-clone';

var arr = [1, 2, 3];
var subObj = { aa: 1 };
var obj = { a: 3, b: 5, c: arr, d: subObj };
var objClone = clone(obj);
arr.push(4);
objClone.d.bb = 2;
obj; // {a: 3, b: 5, c: [1, 2, 3, 4], d: {aa: 1}}
objClone; // {a: 3, b: 5, c: [1, 2, 3], d: {aa: 1, bb: 2}}

just-pluck-it

source

🍦 Try it

npm install just-pluck-it
yarn add just-pluck-it

Pluck a property from each member of a collection

import pluck from 'just-pluck-it';

pluck([{a:1, b:2}, {a:4, b:3}, {a:2, b:5}], 'a'); // [1, 4, 2]
pluck({x: {a:1, b:2}, y: {a:4, b:3}, z: {a:2, b:5}}, 'a'); // {x: 1, y: 4, z: 2}

just-flush

source

🍦 Try it

npm install just-flush
yarn add just-flush

Returns a copy of an array or object with null/undefined members removed

import flush from 'just-flush';

flush([1, undefined, 2, null, 3, NaN, 0]); // [1, 2, 3, NaN, 0]
flush([true, null, false, true, [null], undefined]); // [true, false, true, [null]]
flush({a: 2, b: null, c: 4, d: undefined}); // {a: 2, c: 4}
flush('something'); // undefined
flush(); // undefined

Objects

just-extend

source

🍦 Try it

npm install just-extend
yarn add just-extend

Extend an object

import extend from 'just-extend';

var obj = {a: 3, b: 5};
extend(obj, {a: 4, c: 8}); // {a: 4, b: 5, c: 8}
obj; // {a: 4, b: 5, c: 8}

var obj = {a: 3, b: 5};
extend({}, obj, {a: 4, c: 8}); // {a: 4, b: 5, c: 8}
obj; // {a: 3, b: 5}

var arr = [1, 2, 3];
var obj = {a: 3, b: 5};
extend(obj, {c: arr}); // {a: 3, b: 5, c: [1, 2, 3]}
arr.push(4);
obj; // {a: 3, b: 5, c: [1, 2, 3, 4]}

var arr = [1, 2, 3];
var obj = {a: 3, b: 5};
extend(true, obj, {c: arr}); // {a: 3, b: 5, c: [1, 2, 3]}
arr.push(4);
obj; // {a: 3, b: 5, c: [1, 2, 3]}

extend({a: 4, b: 5}); // {a: 4, b: 5}
extend({a: 4, b: 5}, 3); {a: 4, b: 5}
extend({a: 4, b: 5}, true); {a: 4, b: 5}
extend('hello', {a: 4, b: 5}); // throws
extend(3, {a: 4, b: 5}); // throws

just-merge

source

🍦 Try it

npm install just-merge
yarn add just-merge

Shallow assign. Like just-extend but without deep copy option.

import merge from 'just-merge';

let obj = {a: 3, b: 5};
merge(obj, {a: 4, c: 8}); // {a: 4, b: 5, c: 8}
obj; // {a: 4, b: 5, c: 8}

let obj = {a: 3, b: 5};
merge({}, obj, {a: 4, c: 8}); // {a: 4, b: 5, c: 8}
obj; // {a: 3, b: 5}

let arr = [1, 2, 3];
let obj = {a: 3, b: 5};
merge(obj, {c: arr}); // {a: 3, b: 5, c: [1, 2, 3]}
arr.push[4];
obj; // {a: 3, b: 5, c: [1, 2, 3, 4]}

merge({a: 4, b: 5}); // {a: 4, b: 5}
merge(3, {a: 4, b: 5}); // throws
merge({a: 4, b: 5}, 3); // throws
merge({a: 4, b: 5}, {b: 4, c: 5}, 'c'); // throws

just-values

source

🍦 Try it

npm install just-values
yarn add just-values

Return property values as an array

const values = require('just-values');

values({a: 4, c: 8}); // [4, 8]
values({a: {aa: 2}, b: {bb: 4}}); // [{aa: 2}, {bb: 4}]
values({}); // []
values([1, 2, 3]); // [1, 2, 3]
values(function(a, b) {return a + b;}); // []
values(new String('hello')); // ['h', 'e', 'l', 'l', 'o']
values(1); // throws exception
values(true); // throws exception
values(undefined); // throws exception
values(null); // throws exception

just-entries

source

🍦 Try it

npm install just-entries
yarn add just-entries

Return object entries as an array of [key, value] pairs

import entries from 'just-entries';

// Object:
entries({c: 8, a: 4}); // [['c', 8], ['a', 4]]
entries({b: {bb: 4}, a: {aa: 2}}); // [['b', {bb: 4}], ['a', {aa: 2}]]
entries({}); // []

// Array:
entries([{c: 8}, {a: 4}]); // [[0, {c: 8}], [1, {a: 4}]]
entries(['À', 'mauvais', 'ouvrier', 'point', 'de', 'bon', 'outil'])
// [[0, 'À'], [1, 'mauvais'] ... [6, 'outil']]
entries([]); // []

just-pick

source

🍦 Try it

npm install just-pick
yarn add just-pick

Copy an object but with only the specified keys

import pick from 'just-pick';

var obj = { a: 3, b: 5, c: 9 };
pick(obj, ['a', 'c']); // {a: 3, c: 9}
pick(obj, 'a', 'c'); // {a: 3, c: 9}
pick(obj, ['a', 'b', 'd']); // {a: 3, b: 5}
pick(obj, ['a', 'a']); // {a: 3}

just-omit

source

🍦 Try it

npm install just-omit
yarn add just-omit

Copy an object but omit the specified keys

import omit from 'just-omit';

var obj = {a: 3, b: 5, c: 9};
omit(obj, ['a', 'c']); // {b: 5}
omit(obj, 'a', 'c'); // {b: 5}
omit(obj, ['a', 'b', 'd']); // {c: 9}
omit(obj, ['a', 'a']); // {b: 5, c: 9}

just-is-empty

source

🍦 Try it

npm install just-is-empty
yarn add just-is-empty

Return true if object has no enumerable key values

import isEmpty from 'just-is-empty';
 isEmpty({a: 3, b: 5}) // false
 isEmpty([1, 2]) // false
 isEmpty(new Set([1, 2, 2])) // false
 isEmpty((new Map()).set('a', 2)) // false
 isEmpty({}) // true
 isEmpty([]) // true
 isEmpty(new Set()) // true
 isEmpty(new Map()) // true
 isEmpty('abc') // false
 isEmpty('') // true
 isEmpty(0) // true
 isEmpty(1) // true
 isEmpty(true) // true
 isEmpty(Symbol('abc')); // true
 isEmpty(//); // true
 isEmpty(new String('abc')); // false
 isEmpty(new String('')); // true
 isEmpty(new Boolean(true)); // true
 isEmpty(null) // true
 isEmpty(undefined) // true

just-is-circular

source

🍦 Try it

npm install just-is-circular
yarn add just-is-circular

Return true if object has a circular reference NOTE: not supported in IE or microsoft edge

import isCircular from 'just-is-circular';
const a = {};
a.b = a;
isCircular(a); // true

const a = {};
a.b = {
  c: a
};
isCircular(a); // true

const a = {};
a.b = {
  c: 4
};
isCircular(a); // false

const a = [];
a.push(a);
isCircular(a); // true

isCircular({}); // false
isCircular('hi'); // false
isCircular(undefined); // false

just-is-primitive

source

🍦 Try it

npm install just-is-primitive
yarn add just-is-primitive

Determine if a value is a primitive value

import isPrimitive from 'just-is-primitive';
isPrimitive('hi') // true
isPrimitive(3) // true
isPrimitive(true) // true
isPrimitive(false) // true
isPrimitive(null) // true
isPrimitive(undefined) // true
isPrimitive(Symbol()) // true
isPrimitive({}) // false
isPrimitive([]) // false
isPrimitive(function() {}) // false
isPrimitive(new Date()) // false
isPrimitive(/a/) // false

just-filter-object

source

🍦 Try it

npm install just-filter-object
yarn add just-filter-object

Filter an object

import filter from 'just-filter';

// returns a new object containing those original properties for which the predicate returns truthy
filter({a: 3, b: 5, c: 9}, (key, value) => value < 6); // {a: 3, b: 5}
filter({a1: 3, b1: 5, a2: 9}, (key, value) => key[0] == 'a'); // {a1: 3, a2: 9}
filter({a: 3, b: 5, c: null}, (key, value) => value); // {a: 3, b: 5}

just-map-object

source

🍦 Try it

npm install just-map-object
yarn add just-map-object

Map an object, passing key and value to predicates

import map from 'just-map-object';

// DEPRECATED: use just-map-values
map({a: 3, b: 5, c: 9}, (key, value) => value + 1); // {a: 4, b: 6, c: 10}
map({a: 3, b: 5, c: 9}, (key, value) => key); // {a: 'a', b: 'b', c: 'c'}
map({a: 3, b: 5, c: 9}, (key, value) => key + value); // {a: 'a3', b: 'b5', c: 'c9'}```

just-map-values

source

🍦 Try it

npm install just-map-values
yarn add just-map-values

Map an object, predicate updates values, receives (value, key, object)

import map from 'just-map-values';

// predicate updates values, receives (value, key, obj)
map({a: 3, b: 5, c: 9}, (value) => value + 1); // {a: 4, b: 6, c: 10}
map({a: 3, b: 5, c: 9}, (value, key) => value + key); // {a: 3a, b: 5b, c: 9c}
map({a: 3, b: 5, c: 9}, (value, key, obj) => obj.b); // {a: 5, b: 5, c: 5}

just-map-keys

source

🍦 Try it

npm install just-map-keys
yarn add just-map-keys

Map an object, predicate updates keys, receives (value, key, object)

import map from 'just-map-keys';

// predicate updates keys, receives (value, key, object)
map({a: 'cow', b: 'sheep', c: 'pig'}, (value) => value);
  // {cow: 'cow', sheep: 'sheep', pig: 'pig'}
map([4, 5, 6], (value, key) => key + 1); // {1: 4, 2: 5, 3: 6}
map({a: 3, b: 5, c: 9}, (value, key) => key + value); // {a3: 3, b5: 5, c9: 9}
map({a: 3, b: 5, c: 9}, (value, key, obj) => obj.b + value + key);
  // {'8a': 3, '10b': 5, '14c': 9}

just-deep-map-values

source

🍦 Try it

npm install just-deep-map-values
yarn add just-deep-map-values

Returns an object with values at all depths mapped according to the provided function

import deepMapValues from 'just-deep-map-values';

const squareFn = (number) => number * number;
deepMapValues({ a: 1, b: { c: 2, d: { e: 3 } } }, squareFn); // => { a: 1, b: { c: 4, d: { e: 9 } } }

just-reduce-object

source

🍦 Try it

npm install just-reduce-object
yarn add just-reduce-object

Reduce an object

import reduce from 'just-reduce-object';

// applies a function against an accumulator and each key-value pairs of the object
// to reduce it to a single value
reduce({a: 3, b: 5, c: 9}, (acc, key, value, index, keys) => {
  acc[value] = key;
  return acc;
}, {}); // {3: 'a', 5: 'b', 9: 'c'}

reduce({a: 3, b: 5, c: 9}, (acc, key, value, index, keys) => {
  acc += value;
  return acc;
}); // 17

just-safe-get

source

🍦 Try it

npm install just-safe-get
yarn add just-safe-get

Get value at property, don't throw if parent is undefined

import get from 'just-safe-get';

const obj = {a: {aa: {aaa: 2}}, b: 4};

get(obj, 'a.aa.aaa'); // 2
get(obj, ['a', 'aa', 'aaa']); // 2

get(obj, 'b.bb.bbb'); // undefined
get(obj, ['b', 'bb', 'bbb']); // undefined

get(obj.a, 'aa.aaa'); // 2
get(obj.a, ['aa', 'aaa']); // 2

get(obj.b, 'bb.bbb'); // undefined
get(obj.b, ['bb', 'bbb']); // undefined

get(obj.b, 'bb.bbb', 5); // 5
get(obj.b, ['bb', 'bbb'], true); // true

get(null, 'a'); // undefined
get(undefined, ['a']); // undefined

get(null, 'a', 42); // 42
get(undefined, ['a'], 42); // 42

const obj = {a: {}};
const sym = Symbol();
obj.a[sym] = 4;
get(obj.a, sym); // 4

just-safe-set

source

🍦 Try it

npm install just-safe-set
yarn add just-safe-set

Set value at property, create intermediate properties if necessary

import set from 'just-safe-set';

const obj1 = {};
set(obj1, 'a.aa.aaa', 4); // true
obj1; // {a: {aa: {aaa: 4}}}

const obj2 = {};
set(obj2, ['a', 'aa', 'aaa'], 4); // true
obj2; // {a: {aa: {aaa: 4}}}

const obj3 = {a: {aa: {aaa: 2}}};
set(obj3, 'a.aa.aaa', 3); // true
obj3; // {a: {aa: {aaa: 3}}}

// don't clobber existing
const obj4 = {a: {aa: {aaa: 2}}};
set(obj4, 'a.aa', {bbb: 7}); // false

const obj5 = {a: {}};
const sym = Symbol();
set(obj5.a, sym, 7); // true
obj5; // {a: {Symbol(): 7}}

just-typeof

source

🍦 Try it

npm install just-typeof
yarn add just-typeof

Type inferer

import typeOf from 'just-typeof';

typeOf({}); // 'object'
typeOf([]); // 'array'
typeOf(function() {}); // 'function'
typeOf(/a/); // 'regexp'
typeOf(new Date()); // 'date'
typeOf(null); // 'null'
typeOf(undefined); // 'undefined'
typeOf('a'); // 'string'
typeOf(1); // 'number'
typeOf(true); // 'boolean'

just-flip-object

source

🍦 Try it

npm install just-flip-object
yarn add just-flip-object

Flip the keys and values

import flip from 'just-flip-object';

// flip the key and value
flip({a: 'x', b: 'y', c: 'z'}); // {x: 'a', y: 'b', z: 'c'}
flip({a: 1, b: 2, c: 3}); // {'1': 'a', '2': 'b', '3': 'c'}
flip({a: false, b: true}); // {false: 'a', true: 'b'}

just-has

source

🍦 Try it

npm install just-has
yarn add just-has

Return a boolen indicating the existence of a deep property, don't throw if parent is undefined

import has from 'just-has';

const obj = {a: {aa: {aaa: 2}}, b: 4};

has(obj, 'a.aa.aaa'); // true
has(obj, ['a', 'aa', 'aaa']); // true

has(obj, 'b.bb.bbb'); // false
has(obj, ['b', 'bb', 'bbb']); // false

has(obj.a, 'aa.aaa'); // true
has(obj.a, ['aa', 'aaa']); // true

has(obj.b, 'bb.bbb'); // false
has(obj.b, ['bb', 'bbb']); // false

has(null, 'a'); // false
has(undefined, ['a']); // false

const obj = {a: {}};
const sym = Symbol();
obj.a[sym] = 4;
has(obj.a, sym); // true

Arrays

just-cartesian-product

source

🍦 Try it

npm install just-cartesian-product
yarn add just-cartesian-product

Takes an input of an array of arrays and returns their Cartesian product.

import cartesianProduct from 'just-cartesian-product';

cartesianProduct([[1, 2], ['a', 'b']]); // [[1, 'a'], [1, 'b'], [2, 'a'], [2, 'b']]
cartesianProduct([[1, 2], ['a', 'b', 'c']]); // [[1, 'a'], [1, 'b'], [1, 'c'], [2, 'a'], [2, 'b'], [2, 'c']]
cartesianProduct([]); // []
cartesianProduct(); // throws

just-unique

source

🍦 Try it

npm install just-unique
yarn add just-unique

Dedupes an array

import unique from 'just-unique';

unique([1, 2, 3, 2, 3, 4, 3, 2, 1, 3]); // [1, 2, 3, 4]

var a = {a: 3};
var b = {b: 4};
var c = {c: 5};
unique([a, a, b, c, b]); // [a, b, c]

unique([1, '1', 2, '2', 3, 2]); // [1, '1', 2, '2', 3]

// declaring sorted array for performance
unique([1, 1, '1', 2, 2, 5, '5', '5'], true); // [1, '1', 2, 5, '6']

// declaring strings array for performance
unique(['a', 'c', 'b', 'c', 'a'], false, true); // ['a', 'b', 'c']

just-flatten-it

source

🍦 Try it

npm install just-flatten-it
yarn add just-flatten-it

Return a flattened array

import flatten from 'just-flatten-it';

flatten([[1, [2, 3]], [[4, 5], 6, 7, [8, 9]]]);
// [1, 2, 3, 4, 5, 6, 7, 8, 9]

flatten([[1, [2, 3]], [[4, 5], 6, 7, [8, 9]]], 1);
// [1, [2, 3], [[4, 5], 6, 7, [8, 9]]]

just-index

source

🍦 Try it

npm install just-index
yarn add just-index

Return an object from an array, keyed by the value at the given id

import index from 'just-index';

index([{id: 'first', val: 1}, {id: 'second', val: 2}], 'id');
// {first: {id: 'first', val: 1}, second: {id: 'second', val: 2}}
index([{id: 'first', val: 1}, null], 'id'); // {first: {id: 'first', val: 1}}
index([], 'id'); // {}
index([], null); // undefined
index({}, 'id'); // undefined

just-insert

source

🍦 Try it

npm install just-insert
yarn add just-insert

Inserts a sub-array into an array starting at the given index. Returns a copy

import insert from 'just-insert';

insert([1, 2, 5, 6], ['a', 'c', 'e'], 2); // [1, 2, 'a', 'c', 'e', 5, 6]
insert([1, 2, 5, 6], 'a', 2); // [1, 2, 'a', 5, 6]
insert([1, 2, 5, 6], ['a', 'c', 'e'], 0); // ['a', 'c', 'e', 1, 2, 5, 6]
insert([1, 2, 5, 6], ['a', 'c', 'e']); // ['a', 'c', 'e', 1, 2, 5, 6]

just-intersect

source

🍦 Try it

npm install just-intersect
yarn add just-intersect

Return the intersect of two arrays

import intersect from 'just-intersect';

intersect([1, 2, 5, 6], [2, 3, 5, 6]); // [2, 5, 6]
intersect([1, 2, 2, 4, 5], [3, 2, 2, 5, 7]); // [2, 5]  

just-compact

source

🍦 Try it

npm install just-compact
yarn add just-compact

Returns a copy of an array with falsey values removed

import compact from 'just-compact';

compact([1, null, 2, undefined, null, NaN, 3, 4, false, 5]); // [1, 2, 3, 4, 5]
compact([1, 2, [], 4, {}]); // [1, 2, [], 4, {}]
compact([]); // []
compact({}); // throws

just-last

source

🍦 Try it

npm install just-last
yarn add just-last

Return the last member of an array

import last from 'just-last';

last([1, 2, 3, 4, 5]); // 5
last([{a: 1}, {b: 1}, {c: 1}]); // {c: 1}
last([true, false, [true, false]]); // [true, false]
last(); // undefined
last([]); // undefined
last(null); // undefined
last(undefined); // undefined

just-tail

source

🍦 Try it

npm install just-tail
yarn add just-tail

Return all but the first element of an array

import tail from 'just-tail';

tail([1, 2, 3, 4, 5]); // [2, 3, 4, 5]
tail([{a: 1}, {b: 1}, {c: 1}]); // [{b: 1}, {c: 1}]
tail([true, false, [true, false]]); // [false, [true, false]]
tail([]); // []
tail(); // undefined
tail(null); // undefined
tail(undefined); // undefined

just-random

source

🍦 Try it

npm install just-random
yarn add just-random

Return a randomly selected element in an array

import random from 'just-random';

random([1, 2, 3]);
// one of [1, 2, 3], at random

just-shuffle

source

🍦 Try it

npm install just-shuffle
yarn add just-shuffle

Return the elements of an array in random order

import shuffle from 'just-shuffle';

shuffle([1, 2, 3]); 
// array with original elements randomly sorted
shuffle([1, 2, 3], {shuffleAll: true}); 
// array with original elements randomly sorted and all in new postions
shuffle([]); // []
shuffle([1]); // [1]
shuffle(); // throws
shuffle(undefined); // throws
shuffle(null); // throws
shuffle({}); // throws

just-split

source

🍦 Try it

npm install just-split
yarn add just-split

Splits array into groups of n items each

import split from 'just-split';

split([]); // []
split([1, 2, 3, 4, 5]); // [[1, 2, 3, 4, 5]]
split([1, 2, 3, 4, 5, 6, 7, 8, 9], 3); // [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
split([1, 2, 3, 4, 5, 6, 7, 8, 9], '3'); // [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
split(['a', 'b', 'c', 'd', 'e'], 2); // [['a', 'b'], ['c', 'd'], ['e']]
split([1, 2, 3, 4, 5, 6, 7, 8], 3); // [[1, 2, 3], [4, 5, 6], [7, 8]]

just-split-at

source

🍦 Try it

npm install just-split-at
yarn add just-split-at

Splits an array into two at a given position

import splitAt from 'just-split-at';

splitAt([1, 2, 3, 4, 5], 2); // [[1, 2], [3, 4, 5]]
splitAt([{a: 1}, {b: 1}, {c: 1}], -1); // [[{a: 1}, {b: 1}], [{c: 1}]]
splitAt([], 2); // [[], []]
splitAt(null, 1); // throws
splitAt(undefined, 1); // throws

just-sort-by

source

🍦 Try it

npm install just-sort-by
yarn add just-sort-by

Produces a new array, sorted in ascending order

import sortBy from 'just-sort-by';

sortBy([10, 1, 5, 20, 15, 35, 30, 6, 8]); // [1, 5, 6, 8, 10, 15, 20, 30, 35]

sortBy([
  {user: 'fabio', details: {city: "Milan", age: 34}},
  {user: 'max', details: {city: "Munich", age: 29}},
  {user: 'zacarias', details: {city: "Sao Paulo", age: 44}},
  {user: 'robert', details: {city: "Manchester", age: 28}},
  {user: 'klaus', details: {city: "Zurich", age: 38}},
], function(o) {
  return o.details.age;
});

/*
[
  {user: 'robert', age: 28},
  {user: 'max', age: 29},
  {user: 'fabio', age: 34},
  {user: 'klaus', age: 38},
  {user: 'zacarias', age: 44},
]
*/

sortBy([
  {user: 'fabio', age: 34},
  {user: 'max', age: 29},
  {user: 'zacarias', age: 44},
  {user: 'robert', age: 28},
  {user: 'klaus', age: 38},
], 'user');
/*
[
  {user: 'fabio', age: 34},
  {user: 'klaus', age: 38},
  {user: 'max', age: 29},
  {user: 'robert', age: 28},
  {user: 'zacarias', age: 44},
]
*/

just-partition

source

🍦 Try it

npm install just-partition
yarn add just-partition

Elements satisfying predicate added to first array, remainder added to second

import partition from 'just-partition';

partition([1, 5, 2, 4, 3], n => n > 3); // [[5, 4],[1, 2, 3]]
partition(['a', 2, 3, '3'], x => typeof x == 'string'); // [['a', '3'],[2, 3]]
partition([1, 2, 3, 4], x => typeof x == 'number'); // [[1, 2, 3, 4],[]]
partition([1, 2, 3, 4], x => typeof x == 'string'); // [[], [1, 2, 3, 4]]
partition([], n => n > 3); // [[], []]
partition({a: 1, b: 2}, n => n > 1); // throws
partition(null, n => n > 1); // throws
partition(undefined, n => n > 1); // throws

just-permutations

source

🍦 Try it

npm install just-permutations
yarn add just-permutations

Returns all permutations of the length N of the elements of the given Array

import permutations from 'just-array-permutations;

permutations([1, 2, 3]); // [[1, 2, 3], [2, 1, 3], [2, 3, 1], [1, 3, 2], [3, 1, 2], [3, 2, 1]]
permutations([]); // []
permutations(); // throws

just-range

source

🍦 Try it

npm install just-range
yarn add just-range

Generate a range array for numbers

import range from 'just-range';

range(1, 5); // [1, 2, 3, 4]
range(5); // [0, 1, 2, 3, 4]
range(-5); // [0, -1, -2, -3, -4]
range(0, 20, 5) // [0, 5, 10, 15]

just-remove

source

🍦 Try it

npm install just-remove
yarn add just-remove

Removes one array from another

import remove from 'just-remove';

remove([1, 2, 3, 4, 5, 6], [1, 3, 6]); // [2, 4, 5]

just-union

source

🍦 Try it

npm install just-union
yarn add just-union

Returns the union of two arrays

import union from 'just-union';

union([1, 2, 5, 6], [2, 3, 4, 6]); // [1, 2, 3, 4, 5, 6]

just-zip-it

source

🍦 Try it

npm install just-zip-it
yarn add just-zip-it

Returns an array of grouped elements, taking n-th element from every given array

import zip from 'just-zip-it';

zip([1, 2, 3]); // [[1], [2], [3]]
zip([1, 2, 3], ['a', 'b', 'c']); // [[1, 'a'], [2, 'b'], [3, 'c']]
zip([1, 2], ['a', 'b'], [true, false]); //[[1, 'a', true], [2, 'b', false]]

zip(undefined, {}, false, 1, 'foo'); // []
zip([1, 2], ['a', 'b'], undefined, {}, false, 1, 'foo'); // [[1, 'a'], [2, 'b']]

zip([1, 2, 3], ['a', 'b'], [true]); // [[1, 'a', true], [2, 'b', undefined], [3, undefined, undefined]]

just-group-by

source

🍦 Try it

npm install just-group-by
yarn add just-group-by

Return a grouped object from array

import groupBy from 'just-group-by';

groupBy([6.1, 4.2, 6.3], Math.floor); // { '4': [4.2], '6': [6.1, 6.3] }
groupBy([1,2,3,4,5,6,7,8], function(i) { return i % 2}); // { '0': [2, 4, 6, 8], '1': [1, 3, 5, 7] }

Statistics

just-mean

source

🍦 Try it

npm install just-mean
yarn add just-mean

The mean (average) value in an array

import mean from 'just-mean';

mean([1, 2, 3, 2, 4, 1]); // 2.1666666667
mean(3, 2, 1); // 2
mean([4]); // 4
mean(['3', 2]); // throws
mean(); // throws

just-median

source

🍦 Try it

npm install just-median
yarn add just-median

Return the median value of an array of numbers

import median from 'just-median';

median([1, 2, 3, 4, 5]); // 3
median([3, -1, 2]); // 2
median([9, 14, 14, 200, 15]); // 14
median(1, 2, 4, 3); // 2.5
median(['3', 2, 1]); // throws
median(); // throws

just-mode

source

🍦 Try it

npm install just-mode
yarn add just-mode

Return the most frequently occuring number(s)

import mode from 'just-mode';

mode([1, 2, 3, 2]); // 2
mode(4, 4, 1, 4); // 4
mode(100, 100, 101, 101); // [100, 101]
mode(4, 3, 2, 1); // [1, 2, 3, 4]
mode(['1', 2, 2, 1, 2]); // throws
mode(null); // throws

just-percentile

source

🍦 Try it

npm install just-percentile
yarn add just-percentile

Return the value at the given percentile (using linear interpolation)

import percentile from 'just-percentile';

percentile([1, 2, 3], 0); // 1
percentile([1, 2, 3], 50); // 2
percentile([1, 2, 3], 100); // 3

// See https://en.wikipedia.org/wiki/Percentile (linear interpolation method)
percentile([15, 20, 35, 40, 50], 5); // 15
percentile([15, 20, 35, 40, 50], 30); // 20
percentile([15, 20, 35, 40, 50], 40); // 27.5
percentile([15, 20, 35, 40, 50], 95); // 50

percentile(1, 2, 3, 50); // throws
percentile(['1', 2, 3], 50); // throws
percentile([], 50); // throws

just-variance

source

🍦 Try it

npm install just-variance
yarn add just-variance

Return the standard deviation of an array or numeric argument list

import variance from 'just-variance';

variance([1, 2, 3, 2, 4, 1]); // 1.3666666667
variance(3, 2, 1); // 1
variance([100, 100, 100.1, 100]); // 0.0025
variance(1, 2, 3, 4, 5, -6); // 15.5
variance([4]); // throws
variance(['3', 2]); // throws
variance(NaN, NaN); // throws
variance(); // throws

just-standard-deviation

source

🍦 Try it

npm install just-standard-deviation
yarn add just-standard-deviation

Return the standard deviation of an array or numeric argument list

import standardDeviation from "just-standard-deviation";

standardDeviation([1, 2, 3, 2, 4, 1]); // 1.16904519
standardDeviation(3, 2, 1); // 1
standardDeviation([100, 100, 100.1, 100]); // 0.05
standardDeviation(1, 2, 3, 4, 5, -6); // 3.9370039
standardDeviation([4]); // throws
standardDeviation(["3", 2]); // throws
standardDeviation(NaN, NaN); // throws
standardDeviation(); // throws

just-skewness

source

🍦 Try it

npm install just-skewness
yarn add just-skewness

Return the skewness of an array or numeric argument list using Pearson's second skewness coefficient

import skewness from "just-skewness";

// Using Pearson's second skewness coefficient
skewness(3, 2, 1); // 0
skewness([1, 2, 3, 2, 4, 1]); // 0.4276994613841504
skewness(1, 2, 3, 4, 5, -6); // -0.762000762001143
skewness([1, 2, 3, 4, 9]); // 0.7705935588815224
skewness([4]); // throws
skewness(["3", 2]); // throws
skewness(NaN, NaN); // throws
skewness(); // throws

Strings

just-template

source

🍦 Try it

npm install just-template
yarn add just-template

Interpolate a string with variables

import template from 'just-template';

var data = {
  a: {
    aa: {
      aaa: 'apple',
      bbb: 'pear'
    },
    bb: 'orange'
  },
  b: 'plum'
};
template('2 {{a.aa.aaa}}s, a {{a.aa.bbb}}, 3 {{a.bb}}s and a {{b}}. Yes 1 {{a.aa.bbb}}.', data);
// '2 apples, a pear, 3 oranges and a plum. Yes 1 pear.'

just-truncate

source

🍦 Try it

npm install just-truncate
yarn add just-truncate

Truncate a string with a custom suffix

  truncate('when shall we three meet again', 9); // 'when s...'
  truncate('when shall we three meet again', 10, ' (etc)'); // 'when (etc)'
  truncate('when shall we', 15,); // 'when shall we'
  truncate('when shall we', 15, '(more)'); // 'when shall we'
  truncate('when shall we', 10, ' (etc etc etc)'); // ' (etc etc etc)'

just-prune

source

🍦 Try it

npm install just-prune
yarn add just-prune

Prune a string with whole words and a custom suffix

  prune('when shall we three meet again', 7); // 'when...'
  prune('when shall we three meet again', 7, ' (more)'; // 'when (more)'
  prune('when shall we', 15,); // 'when shall we'
  prune('when shall we', 15, ' (etc)'); // 'when shall we'
  prune('when shall we', 7, ' (more)'); // ' (more)'

just-squash

source

🍦 Try it

npm install just-squash
yarn add just-squash

Remove all spaces from a string, optionally remove escape sequences too

  squash('the cat sat on the mat'); // 'thecatsatonthemat'
  squash(' the cat sat on the mat '); // 'thecatsatonthemat'
  squash('\tthe cat\n sat \fon \vthe \rmat '); // '\tthecat\nsat\fon\vthe\rmat'
  squash('\tthe cat\n sat \fon \vthe \rmat ', true); // 'thecatsatonthemat'
  squash(`the cat
sat on the mat`, true); // thecatsatonthemat

just-left-pad

source

🍦 Try it

npm install just-left-pad
yarn add just-left-pad

Add characters to the left of a string such that its total length is n

import leftPad from 'just-left-pad';

leftPad('hello', 9); // '    hello'
leftPad('hello', 3); // 'hello'
leftPad('hello', 9, '.'); // '....hello'
leftPad('hello', 9, '..'); // '....hello'
leftPad('hello', 10, 'ab'); // 'bababhello'
leftPad('hello', 9, '\uD83D\uDC04'); // '🐄🐄🐄🐄hello'
leftPad('hello', 10, '\uD83D\uDC11\uD83D\uDC04'), // '🐄🐑🐄🐑🐄hello'
leftPad('hello', 7, '🐄'), // '🐄🐄hello'
leftPad(null, 7); // throws
leftPad([], 4, '*'); // throws
leftPad('hello', 4, true); // throws
leftPad('hello', -4, true); // throws  
leftPad('hello', 2.3, true); // throws    

just-right-pad

source

🍦 Try it

npm install just-right-pad
yarn add just-right-pad

Add characters to the right of a string such that its total length is n

import rightPad from 'just-right-pad';

rightPad('hello', 9); // 'hello    '
rightPad('hello', 3); // 'hello'
rightPad('hello', 9, '.'); // 'hello....'
rightPad('hello', 9, '..'); // 'hello....'
rightPad('hello', 10, 'ab'); // 'helloababa'
rightPad('hello', 9, '\uD83D\uDC04'); // 'hello🐄🐄🐄🐄'
rightPad('hello', 10, '\uD83D\uDC11\uD83D\uDC04'), // 'hello🐑🐄🐑🐄🐑'
rightPad('hello', 7, '🐄'), // 'hello🐄🐄'
rightPad(null, 7); // throws
rightPad([], 4, '*'); // throws
rightPad('hello', 4, true); // throws
rightPad('hello', -4, true); // throws  
rightPad('hello', 2.3, true); // throws    

just-camel-case

source

🍦 Try it

npm install just-camel-case
yarn add just-camel-case

Convert a string to camel case

  import camelCase from 'just-camel-case';

  camelCase('the quick brown fox'); // 'theQuickBrownFox'
  camelCase('the_quick_brown_fox'); // 'theQuickBrownFox'
  camelCase('the-quick-brown-fox'); // 'theQuickBrownFox'
  camelCase('theQuickBrownFox'); // 'theQuickBrownFox'
  camelCase('thequickbrownfox'); // 'thequickbrownfox'
  camelCase('the - quick * brown# fox'); // 'theQuickBrownFox'
  camelCase('behold theQuickBrownFox'); // 'beholdTheQuickBrownFox'
  camelCase('Behold theQuickBrownFox'); // 'beholdTheQuickBrownFox'
  // all caps words are camel-cased
  camelCase('The quick brown FOX'), 'theQuickBrownFox');
  // all caps substrings >= 4 chars are camel-cased
  camelCase('theQUickBrownFox'); // 'theQUickBrownFox'
  camelCase('theQUIckBrownFox'); // 'theQUIckBrownFox'
  camelCase('theQUICKBrownFox'); // 'theQuickBrownFox'

just-kebab-case

source

🍦 Try it

npm install just-kebab-case
yarn add just-kebab-case

Convert a string to kebab case

  import kebabCase from 'just-kebab-case';

  kebabCase('the quick brown fox'); // 'the-quick-brown-fox'
  kebabCase('the-quick-brown-fox'); // 'the-quick-brown-fox'
  kebabCase('the_quick_brown_fox'); // 'the-quick-brown-fox'
  kebabCase('theQuickBrownFox'); // 'the-quick-brown-fox'
  kebabCase('theQuickBrown Fox'); // 'the-quick-brown-fox'
  kebabCase('thequickbrownfox'); // 'thequickbrownfox'
  kebabCase('the - quick * brown# fox'); // 'the-quick-brown-fox'
  kebabCase('theQUICKBrownFox'); // 'the-q-u-i-c-k-brown-fox'

just-snake-case

source

🍦 Try it

npm install just-snake-case
yarn add just-snake-case

Convert a string to snake case

  import snakeCase from 'just-snake-case';

  snakeCase('the quick brown fox'); // 'the_quick_brown_fox'
  snakeCase('the-quick-brown-fox'); // 'the_quick_brown_fox'
  snakeCase('the_quick_brown_fox'); // 'the_quick_brown_fox'
  snakeCase('theQuickBrownFox'); // 'the_quick_brown_fox'
  snakeCase('thequickbrownfox'); // 'thequickbrownfox'
  snakeCase('the - quick * brown# fox'); // 'the_quick_brown_fox'
  snakeCase('theQUICKBrownFox'); // 'the_q_u_i_c_k_brown_fox'

just-pascal-case

source

🍦 Try it

npm install just-pascal-case
yarn add just-pascal-case

Convert a string to pascal case

  import pascalCase from 'just-pascal-case';

  pascalCase('the quick brown fox'); // 'TheQuickBrownFox'
  pascalCase('the_quick_brown_fox'); // 'TheQuickBrownFox'
  pascalCase('the-quick-brown-fox'); // 'TheQuickBrownFox'
  pascalCase('theQuickBrownFox'); // 'TheQuickBrownFox'
  pascalCase('thequickbrownfox'); // 'Thequickbrownfox'
  pascalCase('the - quick * brown# fox'); // 'TheQuickBrownFox'
  pascalCase('theQUICKBrownFox'); // 'TheQUICKBrownFox'

just-capitalize

source

🍦 Try it

npm install just-capitalize
yarn add just-capitalize

Capitalize the first character of a string

  import capitalize from 'just-capitalize';

/*
  capitalize('capitals'); // 'Capitals'
  capitalize('Capitals'); // 'Capitals'
  capitalize('many words'); // 'Many words'
  capitalize('!exclaim'); // '!exclaim'
*/

just-replace-all

source

🍦 Try it

npm install just-replace-all
yarn add just-replace-all

Replace all occurrences of a string within a string with another string

  import replaceAll from 'just-replace-all';

/*
  replaceAll('hello, world', 'l', 'q'); // 'heqqo, worqd'
  replaceAll('hello, world', 'l', 'qq'); // 'heqqqqo, worqqd'
  replaceAll('hello, world', 'll', 'q'); // 'heqo, world'
  replaceAll('hello, world', '', 'q'); // 'hello, world'
  replaceAll('hello, world', 'l', ''); // 'heo, word'
  replaceAll('hello, world', null, 'q'); // 'hello, world'
  replaceAll('hello, world', 'l'); // throw
  replaceAll('hello, world'); // throw
  replaceAll(); // throw
  replaceAll(null, 'l', 'q'); // throw
  replaceAll('hello, world', null, 'q'); // throw
  replaceAll('hello, world', 'l', null); // throw
*/

Numbers

just-clamp

source

🍦 Try it

npm install just-clamp
yarn add just-clamp

Restrict a number within a range

import clamp from 'just-clamp';

var n = 5;
clamp(1, n, 12); // 5
clamp(3, n, 1); // 3
clamp(8, n, 9); // 8
clamp(0, n, 0); // 0

var n = -5;
clamp(1, n, 12); // 1
clamp(-7, n, -8); // -7

clamp(NaN, n, 8); // NaN
clamp(3, n, NaN); // NaN  
clamp(3, NaN, 8); // NaN    

clamp(undefined, n, 8); // throws
clamp(3, n, 'h'); // throws  
clamp(3, false, 8); // throws 

just-in-range

source

🍦 Try it

npm install just-in-range
yarn add just-in-range

Check if number is within a given range

  import inRange from 'just-number-in-range'

  inRange(2, 1, 10); // true
  inRange(15, 20); // true
  inRange(20, 21, 30); // false
  inRange(30, 21, 30); // false
  inRange(); // throws
  inRange(100); // throws
  inRange("js"); // throws

just-is-prime

source

🍦 Try it

npm install just-is-prime
yarn add just-is-prime

Check if number is prime

  import isPrime from 'just-is-prime;

/*
  isPrime(1); // false
  isPrime(2); // true
  isPrime(17); // true
  isPrime(10); // false
  isPrime(); // throws
  isPrime(null); // throws
  isPrime("js"); // throws
  isPrime({}); // throws
  isPrime(function() {}); // throws
  isPrime([]); // throws
*/

just-modulo

source

🍦 Try it

npm install just-modulo
yarn add just-modulo

Modulo of a number and a divisor

import modulo from 'just-modulo';

modulo(7, 5); // 2
modulo(17, 23); // 17
modulo(16.2, 3.8); // 1
modulo(5.8, 3.4); //2.4
modulo(4, 0); // 4
modulo(-7, 5); // 3
modulo(-2, 15); // 13
modulo(-5.8, 3.4); // 1
modulo(12, -1); // NaN
modulo(-3, -8); // NaN
modulo(12, 'apple'); // NaN
modulo('bee', 9); // NaN
modulo(null, undefined); // NaN

just-random-integer

source

🍦 Try it

npm install just-random-integer
yarn add just-random-integer

Produces a random integer within a given range

import random from 'just-random-integer';

random();
// Returns either 0 or 1
random(5);
// Returns a random integer between 0 and 5 (inclusively)
random(3, 10);
// Returns a random integer between 3 and 10 (inclusively)
random(-5.8, 10.4);
// Returns a random integer between -5 and 10 (inclusively)

Functions

just-compose

source

🍦 Try it

npm install just-compose
yarn add just-compose

Return a function composed of 2 or more functions

import compose from 'just-compose';

const sqRootBiggest = compose(Math.max, Math.sqrt, Math.trunc);
sqRootBiggest(10, 5); // 3
sqRootBiggest(7, 0, 16); // 4

just-curry-it

source

🍦 Try it

npm install just-curry-it
yarn add just-curry-it

Return a curried function

import curry from 'just-curry-it';

function add(a, b, c) {
  return a + b + c;
}
curry(add)(1)(2)(3); // 6
curry(add)(1)(2)(2); // 5
curry(add)(2)(4, 3); // 9

function add(...args) {
  return args.reduce((sum, n) => sum + n, 0)
}
var curryAdd4 = curry(add, 4)
curryAdd4(1)(2, 3)(4); // 10

function converter(ratio, input) {
  return (input*ratio).toFixed(1);
}
const curriedConverter = curry(converter)
const milesToKm = curriedConverter(1.62);
milesToKm(35); // 56.7
milesToKm(10); // 16.2

just-demethodize

source

🍦 Try it

npm install just-demethodize
yarn add just-demethodize

Turn a method into a standalone function; the first arg becomes this

import demethodize from 'just-demethodize';

const trimFn = demethodize(''.trim);
['hello ', ' goodbye', 'hello again'].map(trimFn); // ['hello', 'goodbye', 'hello again']

just-flip

source

🍦 Try it

npm install just-flip
yarn add just-flip

Flip first two arguments of a function

import flip from 'just-flip';

flip(console.log)(1, 2, 3) // 2, 1, 3

import map from 'just-map-object';
import partial from 'just-partial';

const numbers = {x: 5, y: 10};
const flippedMap = flip(map);
const double = partial(flippedMap, (undefined, number) => number * 2);
double(numbers) // {x: 10, y: 20];

just-partial-it

source

🍦 Try it

npm install just-partial-it
yarn add just-partial-it

Return a partial function

import partial from 'just-partial-it';

const cubedRoot = partial(Math.pow, _, 1/3);
cubedRoot(64); // 4

const getRoot = partial(Math.pow, 64);
getRoot(1/2); // 8

just-debounce-it

source

🍦 Try it

npm install just-debounce-it
yarn add just-debounce-it

Return a debounced function

import debounce from "just-debounce-it";

const fn1 = debounce(() => console.log("Hello"), 500);
fn1();
fn1();
fn1();
// 500ms later logs 'hello' once

const fn2 = debounce(() => console.log("Hello"), 500, true);
fn2(); // logs hello immediately
fn2();
fn2();
// 500ms later logs 'hello' once

const fn3 = debounce(() => console.log("Hello"), 500);
fn3();
fn3();
fn3();
fn3.cancel();
// function cancelled before 'hello' is logged

const fn4 = debounce(() => console.log("Hello"), 500);
fn4();
fn4();
fn4();
fn4.flush();
// immediately invoke the debounced function

just-memoize

source

🍦 Try it

npm install just-memoize
yarn add just-memoize

An implementation of the memoize technique

import memoize from 'just-memoize';

const sumByOne = memoize(function(value) {
  return value + 1;
});

sumByOne(10); // Returns value returned by the function
sumByOne(10); // Cache hit!

sumByOne(20); // Returns value returned by the function
sumByOne(20); // Cache hit!

// Custom cache key (key defaults to JSON stringified arguments)
var sum = memoize(function(a, b) {
  return a + b;
}, function(a, b) {
  return `${a}-${b}`;
});

sum(10, 10); // Returns value returned by the function
sum(10, 20); // Returns value returned by the function
sum(10, 20); // Cache hit!

just-memoize-last

source

🍦 Try it

npm install just-memoize-last
yarn add just-memoize-last

A memoize implementation that only caches the most recent evaluation

const memoizeLast = require('just-memoize-last')
const compare = require('just-compare')

const maxValue = memoizeLast(function(arr) {
  return Math.max(...arr)
}, function(a, b) {
  return compare(a, b)
});

maxValue([1,2,3]) // 3
maxValue([1,2,3]) // cache hit!
maxValue([1,3,4]) // 4
maxValue([1,2,3]) // 3

just-random

source

🍦 Try it

npm install just-random
yarn add just-random

Return a randomly selected element in an array

import random from 'just-random';

random([1, 2, 3]);
// one of [1, 2, 3], at random

just-throttle

source

🍦 Try it

npm install just-throttle
yarn add just-throttle

Return a throttled function

import throttle from 'just-throttle';

// no matter how many times the function is called, only invoke once within the given interval
// options: 
// `leading`: invoke  before interval
// `trailing`: invoke afer interval

const fn1 = throttle(() => console.log('hello'), 500, {leading: true});
setInterval(fn1, 400);
// logs 'hello' immediately and then every 500ms

const fn2 = throttle(() => console.log('hello'), 500, {trailing: true});
setInterval(fn2, 400);
// logs 'hello' after 500ms and then every 500ms

const fn3 = throttle(() => console.log('hello'), 500, {leading: true, trailing: true});
// forces trailing to false

const fn4 = throttle(() => console.log('hello'), 500, { leading: false });
fn4();
fn4();
fn4();
fn4.cancel();
// function cancelled before 'hello' is logged

const fn5 = throttle(() => console.log("Hello"), 500);
fn5();
fn5();
fn5();
fn5.flush();
// immediately invoke the throttled function

just-once

source

🍦 Try it

npm install just-once
yarn add just-once

Create a function that can only be invoked once

import once from 'just-once';

const fn = once(() => console.log('hello'));

fn();
// logs 'hello'
fn();
// does nothing

Testing

Run all tests as a single test suite with

npm run test

Cross browser tests (via saucelabs) are in the sauce branch

Contribute!

https://github.com/angus-c/just/blob/master/CONTRIBUTING.md